Diffusion transfer process using an oxidized 4, 6-diamino-ortho-cresol solution



United States Patent 3,241,964 DIFFUSION TRANSFER PROCESS USING AN OXI- DIZED 4,6-DIAMlNO-ORTHO-CRESOL SOLUTION Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware No Drawing. Filed Apr. 10, 1962, Ser. No. 186,345

Claims. (Cl. 96-29) This invention relates to photography and, more par ticularly, to compositions and processes useful in the development of photosensitive silver halide elements.

It is one object of the present invention to provide novel developer compositions and processes employing such novel developer compositions for the development of exposed silver halide emulsions.

A further object of this invention is to provide novel developer compositions particularly useful in diffusion transfer processes and capable of producing high contrast silver transfer images with extremely short exposures.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the compositions prossessing the features, properties and the relation of. elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

It has now been discovered that 4,6-diamino-orthocresol:

HsC N z l l z possesses unusual and unexpected photographic properties if it is oxidized prior to use as a silver halide developing agent.

Although 4,6-diamino-ortho-cresol has been proposed for use as a silver halide developing agent, the photographic art has treated it as a rather unstable compound requiring strict exclusion of air and/or the addition of anti-oxidants or other stabilizing agents to be photographically useful. Such use of 4,6-diamino-ortho-cresol has given interesting results, including relatively high A.S.A. exposure indices, as disclosed and claimed in the copending application of Edwin H. Land, Milton Green and Meroe M. Morse, Serial No. 564,492 (now abandoned and the subject matter of which is incorporated in continuation-in-part application Serial No. 226,547).

It therefore was surprising to discover that extremely high A.S.A. exposure indices could be employed if the 4,6-diamino-ortho-cresol was at least partially oxidized prior to development. The requisite oxidation may be effected by passing air through a solution of 4,6-diaminoortho-cresol before adding it to the rest of the developer composition, or by simply mixing the developer composition while exposed to air and in the absence of an antioxidant such as sodium sulfite.

As noted above, the novel developer compositions of this invention are particularly useful in the formation of silver transfer images by diffusion transfer processes. Such diffusion transfer processes are now well known in the art; see, for example, U.S. Patents Nos. 2,543,181, 2,647,056, etc. In diffusion transfer processes of this type, an exposed silver halide emulsion is treated with a fluid processing composition while in superposed relationship with an image-receiving material. The processing composition develops the exposed silver halide to silver and reacts with unexposed and undeveloped silver halide to form a dilfusible, complex silver salt which is transferred to the image-receiving material where the silver thereof is precipitated to form a positive silver transfor print. The processing composition includes a silver halide solvent, such as sodium thiosulfate, and may also contain a film-forming material, e.g., sodium carboxymethyl cellulose or hydroxyethyl cellulose, for increasing the viscosity of the processing composition. As used herein, the term silver halide solvent refers to reagents which will form a soluble complex with silver halide, as is well known in the art of forming silver images by diffusion transfer.

The image-receiving material preferably contains silver precipitating nuclei which may be dispersed in a suitable matrix in accordance with practices now well known in the art.

The following example is intended to illustrate the preparation of a developer composition in accordance with this invention, and is intended to be illustrative only.

Example 1 g. of 4,6-diamino-ortho-cresol was dissolved in 200 cc. of water and 40 g. of sodium hydroxide. The resulting solution was stirred while exposed to the air and the solution rapidly darkened. 147 cc. of the resulting solution then was added to a composition comprising Water cc 1470 Natrasol 250 (trade name of Hercules Powder Co.

for high viscosity hydroxyethyl cellulose) g 74.7 Sodium hydroxide g 97.2 Sodium thiosulfate g 97.2 S-Nitrobenzimidazole g 1.2 Solution of 4% S-nitrobenzimidazole in 10% aqueous sodium hydroxide cc 40.5

The following example is intended to illustrate the use of the novel developer composition in diffusion transfer processes, and is given for illustrative purposes only.

Example 2 A silver iodobromide emulsion was given a very low level exposure and then processed by spreading the processing composition prepared in Example 1 between the exposed negative and an image-receiving element as said negative and image-receiving element were brought into superposed relationship. The image-receiving element comprised a silver-receptive stratum containing silver precipitating nuclei dispersed in a matrix of colloidal silica coated on a water-impervious base according to the practice described in U.S. Patent No. 2,823,122. After an imbibition period of approximately 10 seconds, the image-receiving element was separated from the negative and contained a high-contrast, high density silver image of relatively coarse grain.

Equivalent overall speeds, i.e., film speeds, of the order of 10,000 or more have been obtained by the procedures of Examples 1 and 2. The expression equivalent overall speed, as set forth herein, indicates generally the correct exposure index or rating to which an A.S.A. exposure meter must be set in order that it give correct exposure data for producing positive prints of satisfactory high quality by the silver transfer process. If the silver halide emulsion is given a uniform, low level exposure prior to photoexposure, the useful film speed obtained above may be increased by a factor of at least two, although at some loss in maximum density. Because of the high film speed, extremely little light is required for exposure. The compositions and processes of this invention therefore are uniquely suited for recording oscilloscope traces, wherein the high contrast and high speed may be effectively employed to reduce oscilloscope intensity and camera aperture, while the resulting transfer images have increased sharpness.

As demonstrated above, employing 4,6-diamino-orthocresol, which has been at least partially oxidized prior to development, produces unexpected photographic results. Obviously, the presence of conventional preservatives or anti-oxidants, e.g., sodium sulfite, preventing such oxidation is undesired. Sulfite-free developer compositions prepared in accordance with this invention have been found to be remarkably stable in storage. Although the presence of sulfite in the usual quantities is undesired, the addition of very small quantities of sodium sulfite, e.g., on the order of 0.03 to 0.04 g. per 100 cc. of developer composition, has been found helpful in insuring uniformity of successive batches, particularly as to their shelf life. Other customary reagents, such as potassium bromide, may be present. It will be noted that 4,6-diamino-ortho-cresol is the only silver halide developing agent in the developer compositions set forth above, and this is the preferred embodiment. If it is desired to add other silver halide developing agents, they should be present only in small amounts.

As noted above, the imbibition period may be extremely short, being on the order of about seconds. A further unobvious and unexpected result flowing from this invention is the discovery that the dark imbibition period may be only a fraction of the total imbibition period, with imbibition being completed outside the dark area, with the negative and image-receiving element still superposed but in an area of actinic light. While the reasons for this are not known, it is believed that the oxidized 4,6- diamino-ortho-cresol may exhibit a desensitizing action upon the unexposed silver halide. Thus, it is possible and practical to perform the diffusion transfer processes of this invention in a self-developing camera of the type sold by Polaroid Corporation, Cambridge, Massachusetts, e.g., Polaroid Land Camera Model 110, retaining the superposed negative and positive in the dark imbibition chamber or zone thereof for only 1 to 3 seconds, and thereafter advancing the still superposed negative and positive into the actinic area around the camera for completion of the imbibition perod, after which the negative and positive are separated. No special opaque supports are needed, sufficient light shielding being provided by the normal paper supports, e.g., baryta-coated paper. In contrast, use of this processing technique with the same silver halide emulsion and the same paper supports, and a high speed processing composition, as in the 3000- speed, Type 47 Polaroid Land Picture Roll, resulted in partial image-reversal and low density due to the resulting fogging of the negative. This processing technique therefore makes it possible to process a large number of exposures in a short total time, a feature particularly useful in scientific applications such as oscilloscope trace recording.

Since certain changes may be made in the above compositions and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process which comprises the steps of:

(a) forming a photographic processing composition comprising water, an alkaline material, a silver halide solvent and 4,6-diamino-ortho-crcsol;

(b) oxidizing at least a substantial portion of said 4,6-diamino-ortho-cresol at some stage during the formation of said photographic processing composition;

(c) applying said photographic processing composition containing oxidized 4,6-diamino-ortho-cresol to a photoexposed silver halide emulsion, thereby effecting development of said photoexposed silver halide emulsion and forming in undeveloped areas of said photoexposed silver halide emulsion a soluble silver complex of said silver halide solvent with undeveloped silver halide;

(d) transferring said soluble silver complex, by diffusion, to a silver-receptive layer in superposed relationship with said photoexposed silver halide emulsion, thereby forming a silver transfer image on said silver-receptive layer, said silver transfer image exhibiting a higher equivalent overall A.S.A. speed and a higher contrast than if said 4,6-diamino-orthocresol had not been so oxidized prior to applying said photographic processing composition to said photoexposed silver halide emulsion.

2. The process of claim 1 wherein said photographic processing composition includes a viscosity-increasing material and is applied by being spread between said photoexposed silver halide emulsion and said silverreceptive layer as said emulsion and said layer are brought into superposed relationship, imbibition is effected in the absence of actinic light for about one to three seconds, and said imbibition thereafter is continued to completion in an area of actinic light.

3. The process of claim 1 including the step of giving said silver halide emulsion a uniform low level exposure prior to said photoexposure.

4. The process of claim 1 including the step of exposing said silver halide emulsion to an oscilloscope trace to form said photoexposed silver halide emulsion.

5. The process of claim 1 wherein said photographic processing composition is substantially free of sodium sulfite.

6. The process of claim 1 wherein said photographic processing composition contains a very small quantity of sodium sulfite on the order of 0.03 to 0.04 gram per cc. of said composition.

7. The process as defined in claim 1 wherein said oxidation is effected by mixing the photographic processing composition while said composition is exposed to air.

8. The process as defined in claim 1 wherein said photographic processing composition comprises, in addition to water and said oxidized 4,6-diamino-ortho-cresol, sodium hydroxide, sodium thiosulfate and hydroxyethyl cellulose.

9. The process as defined in claim 1 wherein said photographic processing composition comprises, in addition to water and said oxidized 4,6-diamino-ortho-cresol, sodium hydroxide, sodium thiosulfate and sodium carboxymethyl cellulose.

10. The process as defined in claim 1 wherein said oxidation is effected prior to adding said 4,6-diamino-orthocresol to the remaining components of said processing composition.

References Cited by the Examiner UNITED STATES PATENTS 3,091,530 5/1963 Green et al 96-29 FOREIGN PATENTS 74,842 7/ 1892 Germany. 860,165 2/1961 Great Britain.

OTHER REFERENCES Hanson: Amer. Photo., 36, January (1944), pp. 12-15.

Mees: The Theory of the Photographic Process, Macmillan, NY. (1959), pp. 563569.

Neblette: Photography-Its Materials and Processes, 6th edition, Van Nostrand, New York (1962), pp. 224-5.

NORMAN G. TORCHIN, Primary Examiner. 

1. THE PROCESS WHICH COMPRISES THE STEPS OF: (A) FORMING A PHOTOGRAPHIC PROCESSING COMPOSITION COMPRISING WATER, AN ALKALINE MATERIAL, A SILVER HALIDE SOLVENT AND 4,6-DIAMINO-ORTHO-CRESOL; (B) OXIDIZING AT LEAST A SUBSTANTIAL PORTION OF SAID 4,6-DIAMINO-ORTHO-CRESOL AT SOME STAGE DURING THE FORMATION OF SAID PHOTOGRAPHIC PROCESSING COMPOSITION; (C) APPLYING SAID PHOTOGRAPHIC PROCESSING COMPOSITION CONTAINING OXIDIZED 4,6-DIAMINO-ORTHO-CRESOL TO A PHOTOEXPOSED SILVER HALIDE EMULSION, THEREBY EFFECTING DEVELOPMENT OF SAID PHOTOEXPOSED SILVER HALIDE EMULSION AND FORMING IN UNDEVELOPED AREAS OF SAID PHOTOEXPOSED SILVER HALIDE EMULSION A SOLUBLE SILVER COMPLEX OF SAID SILVER HALIDE SOLVENT WITH UNDEVELOPED SILVER HALIDE; (D) TRANSFERRING SAID SOLUBLE SILVER COMPLEX, BY DIFFUSION, TO A SILVER-RECEPTIVE LAYER IN SUPERPOSED RELATIONSHIP WITH SAID PHOTOEXPOSED SILVER HALIDE EMULSION, THEREBY FORMING A SILVER TRANSFER IMAGE ON SAID SILVER-RECEPTIVE LAYER, SAID SILVER TRANSFER IMAGE EXHIBITING A HIGHER EQUIVALENT OVERALL A.S.A. SPED AND A HIGHER CONTRAST THAN IF SAID 4,6-DIAMINO-ORTHOCRESOL HAD NOT BEEN SO ORIDIZED PRIOR TO APPLYING SAID PHOTOGRAPHIC PROCESSING COMPOSITION TO SAID PHOTOEXPOSED SILVER HALIDE EMULSION. 